1. Field of the Invention
The invention relates to improvements in or to terminals provided on electrical equipment or the male and female members of a plug connector and intended to receive and to hold the end of an electrical supply or distribution cable.
2. Description of the Prior Art
To fix the end of a cable in a bushing, a great many devices have been devised.
The simplest of them comprise a simple clamping screw, with overlapping head, screwed transversely through the wall of the bushing itself. In order to increase the support surface on the cable and/or not to damage the latter recourse has been had to inserting a small plate between the screw and the cable, which presents however the drawback of preventing the clamping of the plate until it contacts the bushing and hence the use of cables below a certain diameter. These known devices have undergone numerous improvements, for example, a decentering of the bore of the bushing has been contemplated and/or the inclination of the screw for the purpose of increasing the length of engagement of the latter. However, none of these devices provide any really effective holding of the cable nor do they prevent accidental loosening of the screw due to vibration or to creep of the cable.
Therefore in other devices both a clamping means and an elastic locking means have been included.
In a first device of this type, an elastic part, of spring steel for example, is inserted between the cable and the inner surface of the overlapping head of the clamping screw. From the start of screwing the cable is subjected to an increasing elastic pressure, and then the end of the screw comes into contact with the elastic part and commences direct clamping which is continued until locking. The elastic part then assumes a role similar to that of an elastic washer and resists loosening of the screw.
Other devices with clamping and elastic locking are constituted by a screw traversing the wall of the bushing freely through an opening, said screw being in engagement with a nut situated on the outside of the bushing. The nut is held against the bushing either by a non-distorting steel stirrup, or by an elastic steel ring, applied against the lateral surface of the bushing opposite the opening and having facing the latter an aperture designed for the passage of the screw whilst in the first case an elastic washer is interposed between the nut and a flat surface formed on the stirrup and in the second case the ring is applied against the outer surface of the nut.
These devices only ensure mediocre guidance of the screw and their assembly is often difficult since they comprise in the best cases, three elements in addition to the bushing: a ring, a nut and a screw.
When such a device is used as an electrical terminal, the use of a stirrup or of a steel ring causes a current transforming phenomenon which results in heating of the parts and a voltage drop in the conductor.
Moreover, in all known devices of which the plates and/or springs and/or screws are of steel the passage of current is effected principally at the point of contact of the conductor and of the bushing, which, for the most part is formed of cupriferous metal. Now it is quite obvious that any dirt or trace of oxidation in this contact area which is particularly difficult to clean, involves an additional electrical resistance which results in heating and poor current flow.